Implement BF16 scalar quantizer for faiss

[alexanderguzhva]

Corresponding faiss PR: facebookresearch/faiss#3444

/kind improvement

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.04%. Comparing base (3c46f4c) to head (8d5e05c).
Report is 96 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##           main     #570       +/-   ##
=========================================
+ Coverage      0   70.04%   +70.04%     
=========================================
  Files         0       67       +67     
  Lines         0     4597     +4597     
=========================================
+ Hits          0     3220     +3220     
- Misses        0     1377     +1377     

see 67 files with indirect coverage changes

[liliu-z]

Are we trying to align the code with FAISS? If so why we don't just pull new versions?

[alexanderguzhva]

I do it from time to time, while cherry-picking the most important PRs asap

[alexanderguzhva]

@liliu-z fyi, faiss has committed this PR to the baseline

[alexanderguzhva]

superseded by #663